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Physics
Special and General Relativity
Gravitational Lensing: Refraction or Something Else?
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[QUOTE="vanhees71, post: 6515848, member: 260864"] As was stressed before, it is not literally the same to have refraction, which is usually naming the phenomena related to the interaction of the electromagnetic field with matter, i.e., due to scattering of em. waves with charged particles, and empty space is not considered as any kind of matter anymore since Einstein got rid of the aether. Mathematically in some sense there's an analogy, because to describe "lensing" you can use for both usual refraction as well as the "bending of light" by gravitational fields using geometrical optics, which is the eikonal approximation of Maxwell's equations. It turns out that the light rays as defined by geometrical optics follow from Fermat's principle, and in matter-free space within GR, this leads formally to a geodesic equation for "massless particles". Fermat's principle of course is also a valid description of light propation in matter in the eikonal approximation. In this sense mathematically both effects are a bit analogous. [/QUOTE]
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Special and General Relativity
Gravitational Lensing: Refraction or Something Else?
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